Latin: Balaenoptera physalus
Months: April – October
Length: Up to 27 metres
Range: Global distribution, absent from the Arctic Ocean
Threats: Pollution, acoustic disturbance
Diet: Fish and krill
Fin whales are the second largest cetacean species, reaching 27 metres in length when fully grown. They have a streamlined body which is generally dark grey on the top surface, with white throat pleats and white underside. There is a characteristic pale grey ‘blaze’ on the right side of the head and subtle chevron patterns along the back behind the blowholes. Unique among cetaceans, the fin whale’s lower jaw is black on the left side and white on the right side, and is an important identification cue. Their flukes are broad with a distinct median notch and slightly concave trailing edge, and are rarely raised out of the water when diving. The curved dorsal fin is set two-thirds of the way along the back, and is visible shortly after the blow, which is tall and columnar.
Fin whales are among the fastest of the large whales. Despite their enormous size, they are capable of reaching speeds of up to 25 mph and can travel up to 90 miles a day. Fin whales are normally seen alone or in small groups, but can form larger aggregations on their feeding grounds. Fin whales produce loud, low-frequency vocalisations that travel long distances through the water and may be used to communicate with each other. They can dive to depths of over 200 metres, which is deeper than either blue or sei whales. Very little is known about the behaviour of fin whales in general and the rare glimpses of them in the Hebrides are normally of travelling and feeding animals.
HABITAT AND DISTRIBUTION
Fin whales are widely distributed throughout all major oceans but seem to favour coastal and shelf waters between temperate and polar regions. Little is known about their movements and migration, and whilst it is thought that some seasonal migrations take place, they appear to be complex. Sightings in the Hebrides are very rare and generally occur during summer months, suggesting that the whales move into our inshore waters to take advantage of rich food resources at this time.
FOOD AND FORAGING
Fin whales feed on fish species such as herring, mackerel and cod, squid, as well as krill. This diet probably varies between areas and seasons. Huge quantities of food and seawater are taken into the mouth, which then closes to allow water to be pushed through the baleen plates. These stiff structures act like a sieve to catch the prey, and then a huge tongue sweeps the food down whilst the water is expelled. Fin whales in other areas of the world are often seen in coastal and shelf regions, where areas of upwelling and interfaces between mixed and stratified waters provide rich feeding opportunities.
STATUS AND CONSERVATION
The total fin whale population in the North Atlantic is estimated at 35,000 to 50,000; numbers were significantly reduced by whaling activities during the 20th Century. Fin whales are known to carry high levels of bioaccumulating pollutants such as heavy metals and organochlorides (pesticides and industrial chemicals), which accumulate with age and can be transferred between generations via lactation. The health implications of bioaccumulating pollutants in all cetaceans are still poorly understood. Fin whales may also be negatively impacted by noise and disturbance from vessels and other underwater noise, which may mask their social sounds.